Researchers in the UK wanted to learn what impact street lights have on crime and the results of their study are sure to raise eyebrows. Absolutely counterintuitively, the researchers found that vehicle-related thefts actually decreased when street lights were turned off after midnight. Moreover, there was more crime in streets and parking lots with brighter lights.

Shining light on street crime

For some years in the UK, local authorities have introduced so-called “part-night lighting” in some residential urban and rural roads. In these places, the street lights automatically switch off after midnight when there is very little traffic. The idea is to save energy costs and reduce carbon emissions, but local residents weren’t too happy, understandably voicing safety concerns.

Whenever there’s such a case of competing interests, there are benefits and drawbacks that need to be put in balance — but you need hard evidence and good data.

This is why researchers from the London School of Hygiene and Tropical Medicine and University College London (UCL) set out to investigate the relationship between crime and part-night lighting. For their study, the researchers looked at three types of street lighting: part-night lighting, dimming lights after midnight, and bright lights kept on consistently throughout the entire night. Even smaller segments of streets and their reported criminal activity were tracked in order to see whether changes in lighting on a particular street increased or decreased crime in other nearby streets.

Overall, the data crunched by the researchers spanned ten years. According to the results, there was no link between changes in street lighting and violence or residential burglary. But when the researchers looked at thefts from parked vehicles, they were surprised to find that crime actually dropped after part-night lighting was instated. There was also a slight drop in the theft of vehicles, but this reduction was deemed statistically insignificant.

The other interesting finding was that where thefts from cars dropped on one street, crime increased in adjacent well-lit streets. It seems like changes in street lighting caused a displacement, with crime counterintuitively increasing by 50% in the most brightly lit areas to compensate for the drop in thefts in the dark streets. However, not all thefts were displaced so the part-night lighting changes actually led to a net reduction in crime. There was no evidence that white lighting was significantly associated with changes in any type of night-time crime examined by the researchers, the authors reported in the Journal of Quantitative Criminology.

“Research studies such as this can help us to better understand crime and security issues. The study findings suggest that energy-saving street lighting adaptations have not increased crime in the streets studied. This is very encouraging but it is important to note that it does not mean that this will be the case under all conditions, and so changes to lighting should be managed carefully,” said Dr. Lisa Tompson, who conducted the research at UCL but is now based at The University of Waikato.

What can explain these odd findings though? Dr. Phil Edwards, an Associate Professor and statistician at the London School of Hygiene & Tropical Medicine, shared his opinion:

“We didn’t set out to find the reasons for the observed changes, but it is possible that when lighting is switched off after midnight, offenders consider that the costs of committing a crime, such as using a torch would likely raise suspicion among residents and risk being witnessed, outweigh the benefits.”

“When lighting is switched off after midnight the streets are likely to be in near darkness, which means that any would-be offenders may find it challenging to see if there are any valuable goods left unsecured in vehicles, so offenders may choose to move elsewhere to fulfill their intentions.”

As a caveat, this particular study only looked at only one out of 43 designated areas monitored by the UK police, so the findings may not generalize at the national level. As such, more broad research is required to measure the impact of changes in lighting on crime. Also worth mentioning is that the study did not monitor the psychological effects of changes in light. Even if dark streets and parking lots are safer this way, residents may nevertheless feel less secure and anxious going out at night around their neighborhood.

For now, this study offers some good news. Keeping the lights on when they’re not really needed is a waste of energy and contributes to both carbon and light pollution. Previously, researchers at the UK Centre for Ecology & Hydrology found that LED lights were responsible for the decline of moth caterpillars and other insects, whose numbers dropped by as much as 50% around lit hedgerows and grass margins. So, there may be more benefits than we thought to keeping the lights off.